Organic compounds include more varied materials in comparison with inorganic compounds, and have a possibility that a material that has various functions can be synthesized by an appropriate molecular design. Also, they have features that a molded article such as a film is flexible, and excellent workability is provided by polymerization. Based on these advantages, photonics and electronics using functional organic materials have been attracting attention recently.
For example, examples of an electronic device using an organic compound as a functional organic material include a solar cell, a light-emitting element, and an organic transistor, which are devices utilizing an electric property (carrier transporting property) and an optical property (light absorption or light emission) of the organic compound material, and, among them, the light-emitting element has been showing remarkable progresses.
As a most basic device structure of the light-emitting element, a structure is known, in which a thin film about 100 nm in total, formed by laminating a hole transporting layer comprising a hole transporting organic compound and an electron transporting light-emitting layer comprising an electron transporting organic compound, is interposed between electrodes. By applying a voltage to this element, light emission can be obtained from the electron transporting organic compound that also has a light-emitting property. The structure like this is generally called a single hetero (SH) structure.
It can be said that the light emitting-element in C. W. Tang et al., Applied Physics Letters, Vol. 51, No. 12, 913–915(1987) is based on a functional separation, namely, transportation of holes being conducted by the hole transporting layer, and transportation of electrons and light emission being conducted by the electron transporting layer
Thereafter, for the purposes of further improvement in change in emission spectrum and in decrease in luminous efficiency due to an interaction (for example, formation of exciplex) generated at an interface of laminated layers, the concept of this functional separation has been developed into a concept of a double hetero (DH) structure in which a light-emitting layer is interposed between a hole transporting layer and an electron transporting layer.
In the light-emitting element as described in Chihava Adachi et al., Japanese Journal of Applied Physics, Vol. 27, No. 2, L269–L271(1988), in order to further suppress an interaction generated at the interface, it is preferable to use a bipolar material that has both an electron transporting property and a hole transporting property to form the light-emitting layer.
However, many of organic compounds are monopolar materials, which have either a hole transporting property or an electron transporting property. For example, the material shown in Japanese Patent Laid-Open 2003-40873 is only applied as an electron injecting layer.
It is therefore desired to newly develop an organic compound that has a bipolar property.
It is an object of the present invention to provide an organic compound that has a bipolar property and also a light emitting property, and further has heat resistance. It is also an object of the present invention to provide an organic semiconductor device using the organic compound, particularly a light-emitting element that is capable of reducing device defects such as a dielectric breakdown or improving a light emitting property by using the organic compound material.